Metallocene catalyst systems and their use for olefin polymerization are well known. Metallocene catalysts are single-sited and differently activated compared to conventional Ziegler-Natta catalysts. A typical metallocene catalyst system includes a metallocene catalyst, a support, and an activator. Upon attaching or “fixing” the catalyst to the support, the catalyst is generally referred to as a supported catalyst. For many polymerization processes, supported catalysts are required, and various methods for attaching metallocene catalysts to a support are known in the art. Supports suitable for use with metallocene catalyst are generally porous materials and can include organic materials, inorganic materials and inorganic oxides.
However, many supports contain reactive functionalities. In some instances, these reactive functionalities may deactivate or reduce the activity of the catalyst fixed to the support. When this occurs, the addition of more catalyst to the catalyst system may be necessary to ensure sufficient polymer production during olefin polymerization. Increasing the catalyst concentration in the catalyst system to compensate for activity reduction caused by reactive functionalities is generally undesirable for many reasons. For instance, generally the addition of more catalyst may also require the addition of more activator. As such, increasing the concentrations of both catalyst and activator to overcome the effects of catalyst deactivation by reactive functionalities substantially increases the cost of olefin polymerization.
Hydroxyl groups are an example of a reactive functionality present on some supports which deactivate metallocene catalysts. Hydroxyl groups are present on supports, such as inorganic oxides. An example of an inorganic oxide is silica gel. As such, when using silica gel to support a metallocene catalyst, it is desirable to remove, reduce or render inactive a sufficient number of the hydroxyl groups. Methods of removing or reducing hydroxyl groups include thermal and/or chemical treatments. The removal of hydroxyl groups is known as dehydroxylation.
Thermally treating or heating the support material generally avoids contamination of the support by undesirable chemicals. However, in the case of many porous supports, such as silica gel, heating the support may fail to achieve sufficient dehydroxylation. Chemically treating the support material can be expensive and may result in contamination of the support.
Thus, there remains a need for increasing the activity of supported metallocene catalyst systems. Particularly, there remains a need for improved supported metallocene catalysts wherein the reactive functionalities of the support are reduced and/or deactivated.